This invention relates generally to cap printing devices, and more particularly to an improved silk screen cap printing device.
Caps imprinted with logos are common sights in today's world. These logos impart various messages, from those of athletic organizations to advertisements, promotions, political slogans, and the like. The present invention is an improved cap printing device which can imprint the logo on the front panel of a cap in a high quality manner, free of any distortions. These distortions, which give the cap an unaesthetic appearance, are caused by printing the logo on an unevenly stressed surface. Wrinkles and stretches are caused by stresses, formed while attempting to obtain a completely flat printing surface. Distortion is most evident at the corners of the surface, which tend to be arced and out of alignment.
Printing logos onto caps by using silk screens is well known in the art. Typical cap printing devices are disclosed in U.S. Pat. No. 4,266,476 to Maloof, U.S. Pat. No. 4,381,706 to Harpold, and U.S. Pat. No. 4,590,854 to Anderson. These patents disclose curved platens with curved silk screens. There are numerous problems with these curved platens and screens.
Initially, with a curved screen, the artist must be extremely skilled so as to produce a symmetric design, proportional to the curvature of the caps to be printed. But regardless of the artist's skill, the logos may still be out of proportion as the curvature of the cap may be different from that of the screen on which the artist works or the platen on which the cap is held. Additionally, the logo may have smears and bare spots as the operator can not uniformly ink a curved screen as his hand must bend according to the screen's curvature.
Cap printing devices with flat platens are also known in the art. However, these devices fail to totally flatten the front panel of a cap on the platen, leaving an unevenly stressed, wrinkled or stretched printing surface. The resulting logo, when printed on an unevenly stressed surface, is distorted.
U.S. Pat. No. Re. 32,731 to Jennings attempts to solve this problem by providing a flat platen with a unique blocking device. The blocking device holds the cap in place and attempts to flatten the front panel of the cap on the platen during printing. While this device has yielded better results, the printed logos are still distorted since the front panel of the cap is still not held completely flat on the straight edged platen. Rather, only those surfaces of the cap front panel in contact with the platen edges are flat. Additionally, since the bill rests against a registration plate perpendicular to the platen, additional stresses at the point where the bill meets the front panel may give rise to wrinkles. Some of this additional stress is relieved as part of the sweatband is held between the platen and the plate. However, this sweatband holding mechanism may not relieve all of the stresses on the front panel of the cap because operating the mechanism depends on the operator's judgment. In one instance, the sweatband may not be pulled down enough, causing the front panel near the bill to rise off the platen surface. The logo printed would be distorted or the sweatband may be pulled down too much, causing the fabric to stretch off the platen. The logo printed would again be distorted.
Another problem with the prior art devices is cap alignment on the platen, so as to centrally print the logo on the cap. This alignment is commonly known as registration. Conventional registration is illustrated in U.S. Pat. No. 4,590,580 issued to Anderson, where the cap is manually centered by the machine operator. Blocking as a means of registration is proposed by Maloof, Harpold and Jennings. But the possibilities for an off-center logo due to cap slippage or poor operator placement remain. These problems are even more common when the caps are mass produced quickly.
Still another problem with the prior art devices is that the silk screens are not interchangeable. In these devices an entire frame containing the silk screen has to be removed from the device each time the printing is changed. These frames are rather large and hence cumbersome to manipulate and inconvenient to store.